Pyrochlore-related oxides containing copper and/or silver and resistor compositions thereof

ABSTRACT

Novel polynary oxides of pyrochlore-related crystal structure having Cu and/or Ag ions in the A-site. Powder compositions comprising such novel oxides and dielectric material plus optional components, useful for forming thick-film printed resistors on dielectric substrates; also resistors formed by firing such powder compositions.

United States Patent 1 Bouchard et al.

[4 1 July 22,1975

1 41 PYROCI-ILORE-RELATED OXIDES CONTAINING COPPER AND/OR SILVER ANDRESISTOR COMPOSITIONS THEREOF 175 Inventors: Robert Joseph Bouchard;Donald Burl Rogers, both of Wilmington, Del.

[73] Assignee: E. I. du Pont de Nemours & Co.,

Wilmington, Del.

22 Filed: Jan. 26, 1973 [21] Appl.No.:326,955

[52] U.S. Cl. 252/521; 252/512; 252/514; 252/518", 423/263; 423/593;423/595", 423/598 [51] Int. Cl. H0lb 1/08 [58] Field of Search 252/521,514, 518, 519, 252/512; 423/593, 263, 598, 595

[56] References Cited UNITED STATES PATENTS 3/1945 Barrington 252/512 X1/1947 Quinn 252/512 Primary Examiner-Leland A. Sebastian AssistantE.raminerR. E. Schafer [57] ABSTRACT Novel polynary oxides ofpyrochlore-related crystal structure having Cu and/or Ag ions in theA-site. Powder compositions comprising such novel oxides and dielectricmaterial plus optional components, useful for forming thick-film printedresistors on dielectric substrates; also resistors formed by firing suchpowder compositions.

16 Claims, N0 Drawings PYROCHLORE-RELATED OXIDES CONTAINING COPPERAND/OR SILVER AND RESISTOR COMPOSITIONS THEREOF BACKGROUND OF THEINVENTION The novel compounds of this invention, and powder compositionscontaining the same, are improvements over those disclosed and claimedin Bouchard U.S. Pat. No. 3,583,931 which teaches the benefits ofbismuth and ruthenium and/or iridium in polynary oxides havingpyrochlore-related crystal structure, for electrical resistorapplications, U.S. Pat. No. 3,533,109 to Lewis C. Hoffman teachesresistor compositions comprising such polynary oxides (and relatedpolynary oxides) plus inorganic binder and finely-divided noble metals.Resistor compositions according to these teachings have enjoyedconsiderable commercial success because of the excellent control theyoffer in providing a range of resistors with reproducible values ofresistivity, little affected by temperature or humidity in use, andreadily printed and fired on dielectric supports.

A primary means of establishing the resistivity of a fired resistoraccording to the teaching of Hoffman is to adjust the relativeproportions of polynary oxide, noble metal, and inorganic binder in thecomposition. In general, the unusual properties of the resistor areadjusted toward higher resistivities by increasing the proportion ofbinder and adjusted toward lower resistivities by increasing theproportion of finely divided noble metal. However, increasingly largeproportions of noble metal to polynary oxide also produce an increase inTCR (temperature coefficient of resistance) and obviate many of theadvantages which have led to the gradual replacement of noblemetal/glass compositions (such as the palladium/silver/glasscompositions of DAndrea U.S. Pat. No. 2,924,540) by the moresophisticated polynary oxide containing compositions.

Chemical substitution in the polynary oxide itself has been investigatedas a method for adjusting electrical properties. Thus the patents citedabove contemplate, e.g., the substitution of yttrium, thallium, indium,cadmium, lead or the rare earth metals of atomic number 57-71 inclusivefor some of the'bismuth in Bi Ru O and Bi lr O and platinum, titanium,tin, chromium, rhodium, rhenium, zirconium, antimony or germanium forsome of the ruthenium or iridium. There is a need, however, forcompositions capable of producing resistivities that are substantiallylower than those obtained with Bi (Ru,lr) O while maintaining thedesirably flat temperature response. Such low resistivities are oftenbelow 10 ohms/square, and are preferably in the range l-5 ohms/square.

SUMMARY OF THE INVENTION A portion of the bismuth in Bi (Ru,lr) O andits modified oxides can be replaced by the ions Ag and Cu, withretention of the pyrochlore structure. Ag is univalent and Cu ispresumably univalent, although it is possible that some divalent Cu maybe present. Cu and/or Ag produces a level of electrical conductivitythat extends the utility of previously known compositions.

The polynary oxides of the invention are electrically conductive oxidesof pyrochlore-related crystal structure having the formula I 2-.r 2 7-2wherein:

l. M is at least one of Ag or Cu;

2, 2. M is Bi or a mixture of at least one half Bi plus up to one halfof one or more cations from among a. bivalent Cd or Pb and b. trivalent,Y, T1, In and rare earth metals of atomic number 57-71, inclusive;

3. M" is at least one of a. Ru,

b. 1r, and

c. a mixture of at least three-fourths of at least one of Ru and Ir andup to one-fourth of at least one of Pt, Ti and Rh;

4. x is in the range 0.10 to 0.60; and

5. zis in the range 0.10 to 1.0, and is equivalent to the sum ofmonovalent cations M and half of divalent cations in the polynary oxide.

Preferred polynary oxides are those wherein X is in the range 0.10 to0.5, and include Ag Bi Ru- O go.5 0.15 o.15 2 6.5. go.s o.s 2 s.s o.- 51.5 2 6.5.

Also a part of this invention are improved powder compositions usefulfor producing on dielectric substrates thick-film (printed) resistors oflow resistivity. Powder compositions of polynary oxides plus dielectricmaterial are known, with optical constituents such as noble metalpowders (platinum, gold, etc.); binary oxides such as Co O etc., asdisclosed in Hoffman, U.S. Pat. No. 3,553,109; CdO as disclosed inSchubert U.S. Pat. No. 3,560,410; and inert liquid vehicle. The im--proved powder compositions of this invention are those wherein thepolynary oxide is a copper and/or silvercontaining polynary oxide ofthis invention as described above.

Also of this invention are electrical elements, such as resistorscomprising a dielectric substrate on which such powder compositions havebeen deposited (as by known screen or stencil printing techniques) andthen fired (sintered) to produce an electrically continuous unit.

DETAILED DESCRIPTION OF THE INVENTION In its simplest embodiment thisinvention consists of the pyrochlore-type oxides of formula M1Bi2',(Ru,lr)-

O-, wherein improved conductivity results from the replacement of partof the Bi ions by ions of Ag or Cu.

The univalent ions Ag, Li and Na have heretofore been known in certainelectrically insulating pyrochlore-type structures. Cu has not beenknown toparticupate in.

compositions of pyrochlore-type structures. 8

1n the prototype pyrochlore formula A B O-, re-

placement of a trivalent cation by a univalent one requires thatstoichiometry be maintained by an equivalent oxygen deficiency (z =ar).In the more complex situation where both univalent and bivalent cationsare substituted, stoichiometry will require a formula A 9 preciatedfurthermore that small departuresfrom exact stoichiometry may frequentlybe expected when a small (Ru,lr) disclosed in the'earlier patent citedabove, as

well as the much smaller variations that resultfrom well recognizedcrystal defects. A substantially greater degree of. substitution forbismuth or a substantially greater oxygen deficiency 2 than given in thepreceding formula or the claims are not conducive to obtaining asingle-phase pyrochlore structure which makes possible the highconductivity of these oxide compositions. On the other hand it will beappreciated that very minor amounts of the univalent metals Ag and Cumight be substituted into the known pyrochlore compositions withoutproducing a substantial effect on the properties.

As indicated above, while it is thought that the copper ions in thepolynary oxides of the present invention are univalent, this is notlimiting. In fact, it is possible that some of the copper may bedivalent. Likewise, while heretofore it has not been possible tosubstitute more Ag or Cu in the pyrochlore than the amount claimed, itis recognized that under different conditions greater amounts of Ag orCu might be possible.

The complex oxides of this invention are prepared by heating togetherthe requisite oxides or the readily oxidizable metals or salts whichprovide a source of the particular elements. Reaction should be carriedout under oxidizing conditions at a temperature ranging from about 600Cto about 1200C. Direct firing in air at ordinary pressure is usuallymost convenient, although an atmosphere of oxygen or super-atmosphericpressures may be advantageous if oxidizable metals in finely dividedform are used as a source of the requisite elements. As a source of theunivalent cation essential to this invention finely-divided silver orcopper may be used, but repeated grinding and firing in an oxygen-richenvironment should then be used to insure complete oxidation. Thepreferred source of silver is AgNO which is easily converted to theoxide under firing conditions. Cu O is preferred as the source ofunivalent copper. Thorough grinding together of the reacting componentsassists in promoting complete reaction which is usually obtained intimes between an hour or less (e.g., 15 min.) and a day. Silica orporcelain vessels may be used, but Pt vessels are preferred at hightemperature to avoide any contamination. The completion of reaction isconveniently judged by obtaining a single phase X-ray diffractionpattern corresponding to the pyrochlore structure. Electricalconductivity may be determined on pressed compacts of the powdered oxideor, more functionally, on composites of the oxide product with lowmelting glasses in the proportion desired to form electrical resistorelements.

The resistor compositions of the present invention are characterized inthat some or all of the polynary oxide in polynary oxide/dielectricpowder compositions is the Ag or Cu polynary oxide of the presentinvention. The novelty herein resides in the use of these novel polynaryoxides. Optional additives may be added to the powder compositions, suchas those disclosed in Schubert U.S. Pat. No. 3,560,410; Hoffman U.S.Pat. No. 3,553,109; Popwich U.S. Pat. No. 3,630,969; and Bouchard U.S.Pat. No. 3,681,262.

Normally the powder compositions contain 5-90 percent polynary oxide and10-95 percent dielectric material, the relative proportions selecteddepending upon electrical properties desired in the final resistor. Thepresence (and amount) of optional additives are determined by similarconsiderations. Generally, up to 10 percent of optional binary oxide maybe present (CdO, V 0 Cr O Mn O Fe;,O,, C0 0 MO, and CuO) and up to 69percent noble metal powder. When the powder composition is to bedispersed in an inert liquid vehicle, the type and amount of vehicle isa matter of selection by one skilled in the art, the amount of vehiclegenerally being 10-90 percent of the resulting dispersion.

The dielectric material may be any inorganic material which serves tobind the noble metal and oxide(s) to the substrate. The inorganic bindercan be any of the glass frits employed in resistor compositions for thisgeneral type. Such frits are generally prepared by melting a glass batchcomposed of the desired metal oxides, or compounds which will producethe glass during melting, and pouring the melt into water. The coarsefrit is then milled to a powder of the desired fineness. The patents toLarsen and Short, U.S. Pat. No. 2,822,279, and to Hoffman, U.S. Pat. No.3,207,706, describe some frit compositions which can be employed eitheralone or in combination with glass wetting agents such as bismuth oxide.Typical frit compositions usable as binders in the compositions of thisinvention include borosilicate glasses such as lead borosilicate,cadmium borosilicate and similar borosilicates. Also, mixtures ofvarious inorganic binders may be used.

Noble metals comprise the free metallic component of the resistorcompositions of this invention. These include gold, silver, platinum andpalladium.

The compositions are used to produce thick film resistors as disclosedin the Hoffman, Schubert, Bouchard and Popowich patents cited above;printing may beby conventional screen or stencil techniques withoptional inert liquid vehicle, as therein described; firing techniquesare similarly described therein. The above patents are thus incorporatedby reference herein.

Generally, application of the resistor composition in paint or pasteform to the substrate may be effected in any desired manner. It willgenerally be desired, however, to effect the application in precisepattern form, which can be readily done in applying well-known screenstencil techniques or methods. The resulting print or pattern will thenbe fired in the usual manner at a temperature from about 650-950C. in anair atmosphere employing the usual firing lehr.

The components of the powder composition are finely divided so that theymay be screen printed; generally, the average particle size is less than20 microns.

1n the examples and elsewhere in 'the specification and claims, allparts, percentages and ratios are by weight, unless otherwise stated.X-ray measurements were made using a Norelco diffractometer.

Resistances were determined with a Non-Linear Systems Series X-lOhmmeter.

Fired resistor film thicknesses were measured using a Brush lnstrumentsDiv. (Clevite Corp.) Surfanalyzer. The thickness, nominally one mil, wasnormally less than one mil; sheet resistivity (ohm/square/mil) wasdetermined by multiplying the resistance of the x200 mil resistor paidby the actual thickness, and dividing by two.

EXAMPLE 1 AgBiRu O Sufficient reactants are fired to produce AgBiRu Obut a hetergeneous product was obtained. 0.2666 g. finely divided Ag,0.5757 g. Bi O and 0.6577 g. RuO were ground together in an automaticmortar for 30 minutes, pressed into a pellet, and fired in a porcelaincrucible open to air for 16 hours at 850C. The hard. black pellet whichresulted was shown by X-ray to contain a phase having a cubicpyrodifferent reaction conditions. I

chlore-type structure along with some remaining RuO and Ag. A similarmixture heated in porcelain at 950C. for 24 hours in air produced ablue-black product having a more crystalline pyrochlore X-ray patternwith a cubic cell constant, a,,, about 1024A. significantly 5 smallerthan that known for Bi Ru- O 1030A). Thus, AgBiRu o was not formed underthese conditions. although it is possible that such polynary oxideswhere x is 1.0 can be formed under more stringent and/r EXAMPLE 2 Ag BiRu O 0.1818 g. AgNO, 0.7484 g. Bi O and 0.5698 g. RuOg were groundtogether in an automatic mortar for 30 minutes, pressed into a pellet,and fired to 950C for 16 hrs. in an open Pt crucible in air. The blackproduct had a single phase x-ray pattern corresponding to the pyrochlorestructure; the cell constant, a,,, was 10.27A.

EXAMPLE 3 Cu ,=,Bi Ru O 0.0823 g. Cu O, 0.8045 g. Bi O and0.6l27 g. RuOwere ground together in an automatic mortar for 30 minutes, pressed intoa pellet, and

mixed with 14 parts powdered glass frit and 20 parts of an organicvehicle composed of 90 percent ethylcellulose and 10 percent terpineoland screen-printed onto prefired alumina substrates; the resultantstructure was dried at 100C. for 10 minutes, fired slowly to 850C. for10 minutes and then slowly brought back to room temperature. Thecomplete cycle took one hour. The resultant resistor pad was 100 X 200mils and about 1 mil thick. The glass frit consisted of (wt. percent)25.7 percent PbO. 20.1 percent B 0 19.7 percent SiO- 7.9 percent A1 024.1 percent ZnO, 2.2 percent ZrO- and 0.3 percent Na O. For comparativepurposes the pyrochlore Bi Ru O described in US. Pat. No. 3,583,931 wasalso tested, with and without free metal powder.

The data reported in Table I are the average of quadruplicate samples.The best conductivity (lowest resistivity) was obtained using asconductor compositions the products of this invention, (b), (c), and (f)in Table I. The conductivity is very much greater than for Bi2RuzO1composition (a) of Table 1), and, surprisingly, greater even than whenan equivalent amount of either metallic element, both excellentelectrical conductors, is directly added to the composition as incompositions (d) and (e) of Table l. The change in resistance (AR),after standing for 42 hours under no electrical load at ambienttemperature and humidity can be quite small, as seen in Table I.

TABLE 1 Fired Resistor Conductive Phase(s) wt.'7( Thickness (mils)Rcsistivit \'(ohms/sq) AR (/1) (a) Bi. .Ru O; (Comparative) 66 0.85165.7 1.14 (h) Ag,, -Bi, -,Ru O (Ex. 2) 66 0.70 16.8 3.71 (c) Cu i,-,Ru- ,O.; (Ex. 3) 66 0.85 16.3 5.63 (d) Bi Ru O (Comparative) 61.2 0.8071.3 0.84

Ag 4.8 (e) Bi Ru O (Comparative) 63.1 0.70 28.9 0.30

. Cu 2.9 guj uJs uJs z tm 4) 66 04x EXAMPLE 4 EXAMPLE 6 Ag Gd Bi Ru o0.2566 g. AgNO 0.4108 g. Gd O 0.5280 g. Bi O and 0.8043 g. RuO wereground together in an automatic mortar for minutes, and fired to 1 100Cin air in an open Pt crucible. The black product had an x-ray patterncorresponding to the pyrochlore structure (cell constant, a,,, of10.26A) along with a small amount of impurity.

The tests in Example 5 were duplicated, except that the glass was (wt.percent) 43.5 percent Pb O 4.3 percent Al O 9.8 percent CaO, 4.9 percentB 0 and 37.5 percent SiO parts conductive powder were used, 17 partsglass were used, and 23 parts vehicle were used (see Table 11).

TABLE II Fired Resistor Conductive Phase(s) Wt. 7: Thickness (mils)Resistivity(ohms/sq.) AR (7:)

(a) Bi Ru O; (Comparative) 60 0.70 168.5 0.48 (b) Ag Bi RU O (Ex. 2) 600.70 8.3 l9 (:2) Cu ,-,Bi -,Ru O (Ex. 3) 60 0.80 5.0 0.16 (d) Bi Ru O(Comparative) 55.6 0.65 32.2 0.26

Ag 4.4 (e) Bi- Ru- O; (Comparative) 57.4 0.80 15.0 016 Cu 2.6 (f) Ag GdBi Ru o (EX. 4) 60 0.95 6.8 025 EXAMPLE 5 The results of Example 6 aresimilar to those of Example 5, except that the resistivity is lower withthe The polynary oxides of the present invention are useglass Of Example6. It ShOulCl be emphasized that these ful as components ofscreen'printable resistor compositions, as shown herein. The oxides (andoptional free metal powder), total conductive phase 66 parts, were lowresistivities are obtained without the addition of any noble preciousmetal powder, a result heretofore unobtainable. It is also obvious thatthere are a wide number of glass compositions, some of which may giveeven lower resistivities.

EXAMPLE 7 Ag Gd BiRu O g. AgNO Gd O 0.6905 Bi- O and 0.7888 g. Ru0 wereground together for 30 minutes in an agate motar and pestle. The groundmixture was fired to l000C. for l6 hours in an open Pt crucible in air.The black product had a pyrochlore-related x-ray pattern (cell constant.a. 10.25A) plus a trace of unreacted RuO The polynary oxides of thepresent invention may be used as resistors, electrodes, etc. Anadvantage of the compounds of this invention is that a higher percentageof glass can be tolerated in compositions thereof to obtain the sameresistivity as conductor compositions known in the art. This is anadvantage because in general, higher glass contents give smoother, morestable resistors.

The invention claimed is:

1. Electrically conductive polynary oxides of pyrochlore-related crystalstructure having the formula l. M is at least one of Ag or Cu;

2. M is Bi or a mixture of at least one half Bi plus up to one half ofone or more cations from among a. bivalent Cd or Pb and b. trivalent Y,Tl, In and rare earth metals of atomic number 57-71, inclusive;

3. M" is at least one of a. Ru,

b. lr, and

c. a mixture of at least three-fourths of at least one of Ru and [r andup to one-fourth of at least one of Pt, Ti and Rh;

4. x is in the range 0.10 to 0.60 and 5. zis in the range 0.10 to 1.0,and is equivalent to the sum of monovalent cations M and half ofdivalent cations in the polynary oxide.

2. Polynary oxides of claim 1 wherein x is in the range 0.10 to 0.5.

3. Polynary oxides of claim 2 wherein M is Ag.

4. Polynary oxides of claim 3 having the approximate formula 5. Polynaryoxides of claim 3 having the approximate formula go.s o.1s onn a as- 6.Polynary oxides of claim 3 having the approximate formula 7. Polynaryoxides of claim 2 wherein M is Cu.

8. Polynary oxides of claim 7 having the approximate formula os ns z as'9. A powder composition comprising the polynary oxides of Claim 1 anddielectric material, useful for producing low resistivity resistors ondielectric substrates.

10. A powder composition comprising the polynary oxides of claim 2 anddielectric material, useful for producing low resistivity resistors ondielectric substrates.

11. A powder composition comprising the polynary oxides of claim 3 anddielectric material, useful for producing low resistivity resistors ondielectric substrates.

12. A powder composition comprising the polynary oxides of claim 4 anddielectric material, useful for producing low resistivity resistors ondielectric substrates.

13. An electrical element comprising a dielectric substrate having firedthereon the composition of claim 9.

14. An electrical element comprising a dielectric substrate having firedthereon the composition of claim 10.

15. An electrical element comprising a dielectric substrate having firedthereon the composition of claim ll.

16. An electrical element comprising a dielectric substrate having firedthereon the composition of claim 12.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,896,055

DATED 1 July 22, 1975 'NVENTOR(S) 3 Robert Joseph Bouchard; Donald BurlRogers It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below;COLUMII LINE ERROR CORRECTION a v I n l 65 .i M M o M M M 0 2 l3 zis zis 2 24 optical optional +3 +4 +3 +4 2 49 A B 0 A B 0 A B O A A A B O 255 AX Y "Y 2 X y 2-x-y 2 7-2 3 55 Popwich Popowich 6 21 Bi Ru 0composition Bi Ru 0 (composition Q 2 2 7 2 2 7 I II M I II 7 23 MXM 2+x2 7+z 'X 2-x 2 7-2 7 38 zis z is I I Signed and Scaled thisTwenty-eighth Day of June 1977 [SEAL] Q Arrest:

RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner oj'Patenlsand Trademarks

1. ELECTRICALLY CONDUCTIVE POLYNARY OXIDES OF PYROCHLORERELATED CRYSTALSTRUCTURE HAVING THEFORMULA
 1. M IS AT LEAST ONE OF AG OR CU,
 2. M'' ISBI OR A MIXTURE OF AT LEAST ONE HALF BI PLUS UP TO ONE HALF OF ONE ORMORE CATIONS FROM AMONG A. BIVALENT CD OR PB AND B. TRIVALENT Y, TL, INAND RARE EARTH METALS OF ATOMIC NUMBER 57-71, INCLUSIVE,
 2. M'' is Bi ora mixture of at least one half Bi plus up to one half of one or morecations from among a. bivalent Cd or Pb and b. trivalent Y, Tl, In andrare earth metals of atomic number 57-71, inclusive;
 2. Polynary oxidesof claim 1 wherein x is in the range 0.10 to 0.5.
 3. Polynary oxides ofclaim 2 wherein M is Ag.
 3. M'''' is at least one of a. Ru, b. Ir, andc. a mixture of at least three-fourths of at least one of Ru and Ir andup to one-fourth of at least one of Pt, Ti and Rh;
 3. M" IS AT LEAST ONEOF A. RU, B. IR, AND C. A MIXTURE OF AT LEAST THREE-FOURTHS OF AT LEASTONE OF RU AND IR AND UP TO ONE-FOURTH OF AT LEAST ONE OF PT, TI AND RH,4. X IS IN THE RANGE 0.10 TO 0.60 AND
 4. x is in the range 0.10 to 0.60and
 4. Polynary oxides of claim 3 having the approximate formulaAg0.5Bi1.5Ru2O6.5.
 5. Polynary oxides of claim 3 having the approximateformula Ag0.5Gd0.75Bi0.75Ru2O6.5.
 5. z is in the range 0.10 to 1.0, andis equivalent to the sum of monovalent cations M and half of divalentcations in the polynary oxide.
 5. Z IS IN THE RANGE 0.10 TO 1.0, AND ISEQUIVALENT T THE SUM OF MONOVALENT CATIONS M AND HALF OF DIVALENTCATIONS IN THE POLYNARY OXIDE.
 6. Polynary oxides of claim 3 having theapproximate formula Ag0.5Gd0.5BiRu2O6.5.
 7. Polynary oxides of claim 2wherein M is Cu.
 8. Polynary oxides of claim 7 having the approximateformula Cu0.5Bi1.5Ru2O6.5.
 9. A POWDER COMPOSITION COMPRISING THEPOLYNARY OXIDES OF CLAIM 1 AND DIELECTRIC MATERIAL, USEFUL FOR PRODUCINGLOW RESISTIVITY RESISTORS ON DIELECTRIC SUBSTRATES.
 10. A powdercomposition comprising the polynary oxides of claim 2 and dielectricmaterial, useful for producing low resistivity resistors on dielectricsubstrates.
 11. A powder composition comprising the polynary oxides ofclaim 3 and dielectric material, useful for producing low resistivityresistors on dielectric substrates.
 12. A powder composition comprisingthe polynary oxides of claim 4 and dielectric material, useful forproducing low resistivity resistors on dielectric substrates.
 13. Anelectrical element comprising a dielectric substrate having firedthereon the composition of claim
 9. 14. An electrical element comprisinga dielectric substrate having fired thereon the composition of claim 10.15. An electrical element comprising a dielectric substrate having firedthereon the composition of claim
 11. 16. An electrical elementcomprising a dielectric substrate having fired thereon the compositionof claim 12.